How to enlarge my C-disk volume?

I use a Dell laptop - Windows 7. My C-disk has a 58 GB space and my D-disk a 222 GB space.
As the laptop is very slow working, I would like to enlarge the space on C, perhaps taking space from the D-disk can do that.
But nowhere I can find the information how to do this, only info about making the space smaller!

I hope someone of this forum can help me with this problem?
Thanks in advance!

@whs, thanks so much for your reply!
As I am, unfortunately, not an expert with computers, I would like to ask you what to do in order to send you my Disk Management.
I am a Dutch lady with some knowledge, but this goes a bit over my head, you see?
So, I'll wait for your information and then I'll sen you all you need as soon as possible......

And in order to get to Disk Management, go to Start > right click on Computer > Manage > Disk Management. Make sure you set the page to full screen. Then make a snip with the snipping tool which you find in All Programs > Accessories.

How much RAM is currently installed? (you can find this by going to Start>right-click 'Computer'>Properties)

Also, one easy way to improve performance is by minimizing the # of programs that start-up every time you turn the PC on(Most of these run in the background but can really use up lots of resources). You can do this by; Going to Start> in the 'Start Search' field type "msconfig" (w/out quotes), enter> Select 'Startup' tab and click "Disable All" button, now go through the list of programs to find your anti-virus and check that one off (w/checkmark). This will make sure that your anti-virus will be active as soon as your PC boots up.

Hope this helps. Post back with results or if any doubts ask away, there are dozens of good guys here that are willing to help.

Thanks for your reply, too. This afternoon I already did exactly what you adviced me here, and there were no problems found. I also made choices in which programs should be loaded when Windows starts up, so that factor is also dealt with.
There is 4 GB RAM active on my PC. With the program Wise Care 365 I have had it scanned and tuned up. Under ca. 1200 MB it will tune up automatically, so that the rest is for working with other programs. It seemed to me that this was a good choice, don't you think?

This evening I will make a snapshot of the Disk management. On this PC I don't work often, but still I would like to have it working properly.
So, later on I will come back with these details......

I got the Manage Disk info. Now I need to find out how to get this sent to this forum. I miss the time to do all the things that Sarah James has adviced. I need to do this tomorrow.
As I already saw that everything is fine on this info, I wonder if we could start the extending C anyway?
It says the following:
C: Status OK, capacity: 58,59 GB and free space: 17,50 GB --> Start up, change file, crash dump, primary partition
D: Status OK, capacity: 229,63 GB and free space: 223,52 GB --> logical station
Recovery = OK, capacity: 9,77 GB and free space: 4,71 GB --> system, active, primary partition.

Do you think this is enough to know, and that a snapshot is not necessary anymore? I hope so.
If not, I hope to meet you again, tomorrow...?
Thanks in advance for all your efforts!

I got it, I got it! ..... I hope......
I used my Dropbox for finding an url in order to send you an image. That took me more than an hour to find out, but I hope you can look at it now.
As it is here already over 23.00 h, I am going to bed now.
Hope to meet you tomorrow again!

When you say "As the laptop is very slow working". How is it very slow? All the time, when you are browsing, when you are running certain applications or in general all the time? Your disk layout doesn't look like it would cause your laptop to run slow.
Do you have all or some applications installed on "C" drive or do you have some installed on your "D" drive?

Well your dropbox failed. But 58 GB is more than enough to hold your OS (unless you have lots of games loaded).If not, then you can relocate your special folders to D. And you have 17.5 GB free on C anyway ?
So that is not the cause of your slowdown. Maybe just a good cleanup will do it. When was the last time you re-installed the OS ?

Early this morning I started a good clean-up and used several programs. I shifted several programs from C to D with EZ File Transplanter.
And, most of the time I use only Spyware Doctor + antivirus, and for years it works very well, but MBAM showed me there was a trojan in my PC.
After changing files and removing the trojan my PC works much better now, pfffff.....
I am so very glad with all your help, I learnt much again from you, thanks só much!
Have a very nice day!

actually there are some software that can extend your partition directly if you think that window disk manager is not so available. partition wizard is one of these tools. you can extend the disk you want within one simple step. but considering you are not good at computer stuff, be more careful if you want to use these tools. they may destroy your disks and your data. just saying, it is up to you.